From: Quentin Perret <qperret@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: james.morse@arm.com, alexandru.elisei@arm.com,
suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org,
linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
ardb@kernel.org, qwandor@google.com, tabba@google.com,
dbrazdil@google.com, kernel-team@android.com
Subject: Re: [PATCH v2 04/16] KVM: arm64: Optimize host memory aborts
Date: Mon, 26 Jul 2021 14:13:06 +0100 [thread overview]
Message-ID: <YP604j6B1pkhAnT1@google.com> (raw)
In-Reply-To: <87pmv5e529.wl-maz@kernel.org>
On Monday 26 Jul 2021 at 11:35:10 (+0100), Marc Zyngier wrote:
> On Mon, 26 Jul 2021 10:28:53 +0100,
> Quentin Perret <qperret@google.com> wrote:
> > +static int host_stage2_find_range(u64 addr, struct kvm_mem_range *range)
>
> nit: I find 'find_range' a bit odd. We already have found a
> range. We're just trying to narrow it down to something that fits in a
> single block mapping. How about 'host_stage2_adjust_range'?
Ack.
> > +{
> > + u64 granule, start, end;
> > + kvm_pte_t pte;
> > + u32 level;
> > + int ret;
> > +
> > + ret = kvm_pgtable_get_leaf(&host_kvm.pgt, addr, &pte, &level);
> > + if (ret)
> > + return ret;
> > +
> > + if (kvm_pte_valid(pte))
> > + return -EAGAIN;
> > +
> > + if (pte)
> > + return -EPERM;
> > +
> > + do {
> > + granule = kvm_granule_size(level);
> > + start = ALIGN_DOWN(addr, granule);
> > + end = start + granule;
> > + level++;
> > + } while ((level < KVM_PGTABLE_MAX_LEVELS) &&
> > + (!kvm_level_supports_block_mapping(level) ||
> > + start < range->start || range->end < end));
> > +
>
> This expression does my head in. You are trying to find the largest
> block mapping that entirely fits in range, right? Can we just express
> that directly (with a global negation for the purpose of the loop)?
>
> do {
> [...]
> } while (level < KVM_PGTABLE_MAX_LEVELS &&
> !(kvm_level_supports_block_mapping(level) &&
> start >= range->start &&
> end <= range->end));
>
> I personally find this much more readable, because it expresses the
> condition we are looking for rather than a lot of conditions forcing
> us to continue.
>
> You could also use a kvm_mem_range for the iteration, and add a helper
> that checks for the inclusion.
Something like this (untested)?
diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 75273166d2c5..07d228163090 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -234,9 +234,15 @@ static inline int __host_stage2_idmap(u64 start, u64 end,
__ret; \
})
+static inline bool range_included(struct kvm_mem_range *child,
+ struct kvm_mem_range *parent)
+{
+ return parent->start <= child->start && child->end <= parent->end;
+}
+
static int host_stage2_find_range(u64 addr, struct kvm_mem_range *range)
{
- u64 granule, start, end;
+ struct kvm_mem_range cur;
kvm_pte_t pte;
u32 level;
int ret;
@@ -252,16 +258,15 @@ static int host_stage2_find_range(u64 addr, struct kvm_mem_range *range)
return -EPERM;
do {
- granule = kvm_granule_size(level);
- start = ALIGN_DOWN(addr, granule);
- end = start + granule;
+ u64 granule = kvm_granule_size(level);
+ cur.start = ALIGN_DOWN(addr, granule);
+ cur.end = cur.start + granule;
level++;
} while ((level < KVM_PGTABLE_MAX_LEVELS) &&
- (!kvm_level_supports_block_mapping(level) ||
- start < range->start || range->end < end));
+ !(kvm_level_supports_block_mapping(level) &&
+ range_included(&cur, parent)));
- range->start = start;
- range->end = end;
+ *range = cur;
return 0;
}
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next prev parent reply other threads:[~2021-07-26 13:15 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-26 9:28 [PATCH v2 00/16] Track shared pages at EL2 in protected mode Quentin Perret
2021-07-26 9:28 ` [PATCH v2 01/16] KVM: arm64: Introduce helper to retrieve a PTE and its level Quentin Perret
2021-07-26 9:28 ` [PATCH v2 02/16] KVM: arm64: Provide the host_stage2_try() helper macro Quentin Perret
2021-07-26 9:28 ` [PATCH v2 03/16] KVM: arm64: Expose page-table helpers Quentin Perret
2021-07-26 9:28 ` [PATCH v2 04/16] KVM: arm64: Optimize host memory aborts Quentin Perret
2021-07-26 10:35 ` Marc Zyngier
2021-07-26 13:13 ` Quentin Perret [this message]
2021-07-26 13:24 ` Marc Zyngier
2021-07-26 9:28 ` [PATCH v2 05/16] KVM: arm64: Rename KVM_PTE_LEAF_ATTR_S2_IGNORED Quentin Perret
2021-07-26 9:28 ` [PATCH v2 06/16] KVM: arm64: Don't overwrite software bits with owner id Quentin Perret
2021-07-26 9:28 ` [PATCH v2 07/16] KVM: arm64: Tolerate re-creating hyp mappings to set software bits Quentin Perret
2021-07-26 9:28 ` [PATCH v2 08/16] KVM: arm64: Enable forcing page-level stage-2 mappings Quentin Perret
2021-07-26 9:28 ` [PATCH v2 09/16] KVM: arm64: Allow populating software bits Quentin Perret
2021-07-26 9:28 ` [PATCH v2 10/16] KVM: arm64: Add helpers to tag shared pages in SW bits Quentin Perret
2021-07-26 9:29 ` [PATCH v2 11/16] KVM: arm64: Introduce and export host_stage2_idmap_locked() Quentin Perret
2021-07-26 9:29 ` [PATCH v2 12/16] KVM: arm64: Mark host bss and rodata section as shared Quentin Perret
2021-07-28 12:14 ` Quentin Perret
2021-07-26 9:29 ` [PATCH v2 13/16] KVM: arm64: Enable retrieving protections attributes of PTEs Quentin Perret
2021-07-26 9:29 ` [PATCH v2 14/16] KVM: arm64: Refactor protected nVHE stage-1 locking Quentin Perret
2021-07-26 9:29 ` [PATCH v2 15/16] KVM: arm64: Restrict EL2 stage-1 changes in protected mode Quentin Perret
2021-07-26 11:27 ` Marc Zyngier
2021-07-26 12:55 ` Quentin Perret
2021-07-26 9:29 ` [PATCH v2 16/16] KVM: arm64: Make __pkvm_create_mappings static Quentin Perret
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